gen autostart set points

jtdiesel65jtdiesel65 Solar Expert Posts: 140 ✭✭✭
I knew things were getting low because of a long stretch of no sun and mostly cloudy weather, but the other day the volts were 22.8 and an SG reading put it at about 80% discharged. sw4024 gen start set points are 15 min is 22.6, 2 hr set is ~23.5 and 24 hr is ~24.2. I'm trying to figure out why the 2 hr and 24 hr didn't trip.

Its a 1576 AH battery at the 20 hr rate and 4020k of solar. I don't use quiet time. I testing the 15 min start and it worked. I haven't tested the others.

I could understand maybe the 24 hr set point not tripping because the panels provided a voltage (but really no charging to the battery) during the day. What seems odd though is why the 2 hr didn't trip. I suppose it could have tripped and when I found the bat at 22.8, it was 1 minute away from the starting the generator, but I think that means there must be some load to drop the bat from 23.5 to 22.8 in less than 2 hrs. I don't have that kind of load. A mystery here.

What are folks using for set points? I thought the set points were designed for when the system would experience short term loads that caused the bat voltage to dip quickly and then return to it's previous higher level so you wouldn't have the generator starting everytime you turned on the vacuum. With a big battery, I'm not sure those voltage dips occur to the same extent as with a small battery.


  • BB.BB. Super Moderators, Administrators Posts: 29,746 admin
    Re: gen autostart set points

    You might want to look at the 15 minute closer to 23.0 volts (11.5v @ 12 volt). That would probably give you a bit better protection for your battery bank (then there is the whole question if these voltages are temperature compensated or not--The set points should "rise" with "cold batteries").

    You might want to test the SW voltage readings against an (accurate) volt meter... Some of the Xantrex product would display Temp. Compensated readings instead of actual readings (i.e., a battery bank at 23.0 volts and 30F may be actually be at 23.2 volts when read with a "sane" meter). And then you get into the whole question of whether or not the generator set-points are TC or not (or even if the TC is working correctly).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jtdiesel65jtdiesel65 Solar Expert Posts: 140 ✭✭✭
    Re: gen autostart set points


    I set it 23.3. I'll see how that works. The sw has temp compensation, but I'm not sure if it uses it for this. I noticed that it seemed to be working to control voltage as the generator was charging.
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: gen autostart set points

    On our 5548 we have an 1,200 ah battery. I'm using (cut voltages in half):

    24 hr 54.0V
    2 hr 47.0V
    15 min 46.4V
    load start 45 amps @ 0.1 min delay, 25.0 min delay before shutdown

    The reason you don't want your 2 hour delay set too high is because it will prevent nuisance gen start when you don't actually need to be charging the batteries. We run very heavy 240 volt loads with our system and it is not unusual for a fully charged bank to drop below 47.0 volts with the inverter putting out 4-5 kVA. That load might only use 8 kWh of our 58 kWh bank capacity and if the load is on for two hours (like my wife is cooking turkey in her electric range) it would cause the generator to start unnecessarily and charge the bank up when it doesn't have to run. As soon as the load is off the bank recovers back up to more "normal" voltages so the 2 hour timer resets.

    All it takes is for the voltage to go 0.1V over that set point after being below it for 1 hour and 58 minutes, and the timer resets. It is not a cumulative timer. Nor is it temperature compensated. Only the charging is temp compensated.

    If you feel your generator should have started sooner on the 2 hr, then adjust it up a couple tenths.

    And BTW - you have your 24 hr set way too low. It should be set to about 75-80% bank capacity (based on your experience knowing where 75-80% is with the typical loads and RE equipment you got). The purpose of the 24hr timer is to complete a bulk charging cycle that your RE sources failed to complete. That has to be set high enough so that on a "poor" day when the solar and wind power did not get the bank above 80% the generator starts and finishes the job. That makes for happy batteries that live long and prosper. My experience after 9 years this coming June of living without utility power is that the little bit of generator fuel it takes to complete that bulk/absorb when you did not reach that 80% SOC level is way cheaper in the long run than replacing a bank of hard sulfated batteries two years before Their Time. And it's also cheaper than boiling the snot out of them with frequent equalizations to try to "fix" chronic deficit charging.
  • jtdiesel65jtdiesel65 Solar Expert Posts: 140 ✭✭✭
    Re: gen autostart set points

    "24 hr 54.0V"

    What are your absorb and float voltages? Is your 24 hr the same as your float voltage?
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: gen autostart set points

    Absorb is set to 62.0, float at 54.8. The type of batteries we have (lead-calcium grid) require higher charging voltages than most batteries. But you should set the 24 hour timer so if the bank remains in float for 24 consecutive hours it won't re-start the generator. And it should also be set to about 75-80% SOC (based on your experience over time knowing where that setpoint is based on loaded voltage) so that it will start the generator and finishing an incomplete bulk charging cycle.

    Generally, at least with our style batteries, it's considered OK if the bank cycles from 50%-80% SOC for up to a week. And if there's sufficient incoming RE power for it to do that, then having the generator start is unnecessary. But one of two things usually happens after a week of this type of weather conditions due to the weather never being totally stable
    - after a week of this 50-80% SOC cycling we'll either get a really good day and the bank will make it thru a complete absorb cycle
    - or we'll get a bad day when it finally doesn't meet that 24 hour timer voltage and the generator starts and finishes it.

    If you set that 24 hr too high it will nuisance start your generator every single day - probably when you don't really need to have it running. If you set it too low you will run into the problem you described in your first post where you're watching your 2 hr and 15 min timers wondering why the generator hasn't started yet.

    That 24 hr timer is the one that SHOULD start the generator 90% of the time for battery charging (non load-start situations). It means incoming RE power has not been sufficient for 24 consecutive hours to get the bank up to at least 80% and it's time to charge it all the way up.

    The 2 hr timer's primary purpose is to start the generator when you put a heavy load on your inverter for more than 2 hours. The voltage drops under heavy load below that 2 hour setpoint. When the heavy load remains on for that long the bank and RE system needs some help to recover it because the RE system is obviously not meeting the load requirement - and it will not catch it up that day after the load goes off. So the 2 hr fires up the gen and gets the bank recovered so it's not "sacked" after the load goes away.

    The 15 min and 30 second timers are there for very heavy loads that don't exceed the Load Start setting, but cause the bank voltage to drop dramatically because of the very heavy load. The bank may have only been at 65% SOC and you throw a 5 kW load at the inverter. The bank voltage drops very quickly and one of those timers will start the generator to recover it before the voltage drops below LBCO.

    It sounds to me like you are using 2 hr timer for long periods of insufficient RE, and that's not what it's for. The 24 hr should be set to cover that. The 2 hr, 15 min and 30 sec timers are delayed load start timers (based on the fact that bank voltage drops under load) for loads that do not exceed the Load Start setting, but need generator help to keep from "sacking" the bank.

    Hope this helps.

    Another thing on the Load Start setting - this is an overload setting only. Your SW or SW Plus inverter will operate in overload for a certain time - the time based on the internal temperatures of the transformers and FET's - before it shuts down due to over-temp. The SW or SW Plus also has the capability to use BOTH generator and battery power to meet this overload situation. So the Load Amps setting should be set close the max continuous for your inverter model. If the load amps exceed that the inverter will power the load for a time - but it needs generator help for long term power to that load. So the delay on Load Start should be set to a reasonable time that the inverter can power the overload that gives the generator sufficient time to start, warm up and go to full rated load to help the inverter out.

    The Load Start/Amps settings allow shutting the generator off after the load drops below the threshold, after a timed delay. This is for cycling loads like the oven in an electric range, where you don't want the generator to start and stop every time the oven elements cycle on and off. The Load Start/Load Amps setting will NOT do a full bulk/absorb cycle on the bank, as it will shut the generator off when the delay time is met after the load drops below the Load Amps threshold. So the purpose of the Load Amps setting is to allow you to run extremely heavy loads up to the max capacity of BOTH the generator and inverter combined, meaning if you have a 4 kVA inverter and a 4 kVA generator you can power a 8 kVA load without needing a 8 kVA generator.
  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: gen autostart set points

    I doubt this is the cause of your problem but it is worth an easy check;

    Look at the "Battery Actual Volts DC" and the "Battery TempComp Volts DC" (Meters menu 4)
    They should be fairly close. Assuming the BTS sensor is installed and the batteries are colder than "normal room temp" the "Battery TempComp Volts" should be +/- 1 volt lower than the Actual. This will vary depending on the actual temp of the BTS.

    I recently saw an SW system where the BTS was sending a bad signal and the SW saw the TempComp voltage as about +5 higher than actual. The AGS was starting the gen but the bad TempComp reading was causing charging to stop and the AGS was not working properly. I was not on site long enough to see what it was doing over a long period. It seems this could also happen with a BTS installed in a bad place or if rats had built a nest on top of it...etc. (I've seen a cat who chose to bed on top of a battery, on the temp sensor.:p)

    I replaced the BTS and all is now good. If I didn't have a replacement BTS I would have just removed the existing one and temporarily adjusted the charging setpoints.

  • jtdiesel65jtdiesel65 Solar Expert Posts: 140 ✭✭✭
    Re: gen autostart set points


    Winter has caused deep cycling. I think that's why I'm seeing some of my problems. Some settings aren't correct for this. For 10 out of 12 months generator starting isn't an issue.

    Looks like the 24 hr needs to be increased. I'm going to try 24.6. I've also discovered that the max absorb time needs to be increased. 3 hrs isn't getting the SG up to where it should be with deeper cycling.

    I think the BTS is ok. The classics are set for 29.6 v for absorption. I noticed the classics, tri-metric, and SW showed a voltage of 30.0 when in absorb. The SW temp compensated voltage was 29.7. All three bts are next to each other.
  • ChrisOlsonChrisOlson Banned Posts: 1,807 ✭✭
    Re: gen autostart set points
    jtdiesel65 wrote: »
    Looks like the 24 hr needs to be increased. I'm going to try 24.6. I've also discovered that the max absorb time needs to be increased. 3 hrs isn't getting the SG up to where it should be with deeper cycling.

    I think you can set it by experience with your system - there is no real answer because everybody's loads, battery bank size and RE capacity is different. Just keep in mind that the 24 hr timer is the primary "maintenance" timer for your bank. It is the one that should start your generator if the RE system doesn't do the job and keep the bank up to at least 80% SOC every day.

    In your first post where you noted the bat going from 23.5 to 22.8 in less than 2 hrs - well, that's what the 2 hr timer does in a case like that. It starts the generator because the bank voltage is dropping rapidly due to either a larger than normal load, or the fact that the bank was down on SOC and normal loads are causing it to cascade into the dumpster. But if the 24 hr is working right, your bank should never really get that low, except for intermittent heavy loads causing it when the bank is below 80% SOC.

    In your case, if 24.6 still doesn't seem to start the gen when it should to keep the bank nicely maintained, keep bumping it up a couple tenths at a time until you're satisfied with how well the bank is being automatically maintained.

    With our system, when it starts on the 24 hr the gen run time is generally less than an hour. It still doesn't do as good of a job as the RE system does with a nice long absorb time (I have the ending amps in the SW Plus set so it shuts the generator off at 3.5% C). But it keeps the bank up in the winter time so that when you do get a good RE day the RE system is able to "catch up" quicker. When the bank is kept up with the generator over the long run, on the "good" day the RE system doesn't have to pull the bank out of the dumpster to get it to that nice long absorb in the limited amount of sun hours you have. Like I said in my first post on this - the little bit of gen fuel that it takes on the 24 hr timer to finish a bulk charge stage that the RE system didn't complete for the day is generally a lot cheaper in the long run than replacing batteries before their time. That 24 hr timer, properly set, is usually a pretty short run time on the generator because the RE did most of the work and the gen only has to finish it.

    OTOH, the gen run time on the 2 hr timer is major if the bank is indeed that low on SOC. If the generator starts on the 2 hr only due to a heavy load pulling the bank down, the gen run time is usually pretty reasonable because the bank recovers quickly.

    Good luck with it!
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